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Safety and resiliency in Skykomish Valley (Old Cascade Highway washout at Miller River Bridge)

Aerial view showing east fork of the Miller River.

An aerial view of the east fork of the Miller River, the old Miller River Bridge and BNSF railroad trestle. The river dramatically changed course in 2011 during a significant storm. As a result, the Miller River Bridge no longer connects Old Cascade Highway over the river. Larger view (1MB JPG). Map data ©2018 Google Earth. Imagery date: July 24, 2018.

View of the Miller River Bridge from the west bank of the current channel of the river. Photo by Tom Minichillo, King County. Larger view (8MB JPG)

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Historic Old Cascade Highway is a low-traffic county road that winds between Stevens Pass and Grotto in the Skykomish Valley. This narrow, seven-mile-long roadway runs parallel to Highway 2. Formerly a through road, the Old Cascade Highway was permanently closed at the East Fork of the Miller River in 2011 when a section of the roadway that led up to the Miller River Bridge was washed out and destroyed by a significant storm. During that storm the river also changed course. The 100-year-old Miller River Bridge no longer spans the current course of the river. US 2 now provides the sole east-west travel route through the area.

In summer 2022, the Bolt Creek Fire in the Skykomish Valley shut down sections of US 2 and cut off access to many residents and travelers. The Bolt Creek Fire Burn Scar now poses an increased risk of potential flash flooding, debris flows and other types of slides in the area, which could cause more temporary shutdowns on US 2.

King County has received several requests to replace Miller River Bridge and reconnect the Old Cascade Highway to provide alternate east-west access when US 2 is closed. However, there is no quick or easy solution to re-establish the Old Cascade Highway across the East Fork of the Miller River. The old Miller River Bridge cannot be repaired or retrofitted to span the current extent of the river and its migration zone. There are many challenges and high costs to build a new bridge and reconnect the Old Cascade Highway.

The road spans a well-known very active river channel migration area. The river continues to change course and erode the banks. The new bridge would need to be approximately 1000 feet long, over four times longer than the old bridge, to safely span the river and reconnect Old Cascade Highway. A new bridge also would require a large, reinforced support system and extra-deep support foundations to withstand the force and unpredictable migration of the river on a regular basis. Lastly, building this type of bridge in a remote, environmentally sensitive area like Skykomish takes more time and money than typical bridge projects.

Location of the proposed Miller River replacement bridge.

The red line in the photo above shows the location of the proposed Miller River replacement bridge, and how it would connect to Old Cascade Highway. Larger view (618KB JPG)

The estimated cost to reconnect the Old Cascade Highway and build a new, modern bridge that could safely be used for all types of vehicles is up to $60 million (in 2022 dollars). The county was not able to fund a replacement bridge and road reconnection in 2011 and has no additional funding sources to cover the cost today.

Other options suggested by the community, such as a temporary bridge or pedestrian bridge also bring challenges and high costs. Both would require a reinforced support system and extra-deep foundations (like the permanent bridge option) to withstand the force of the river channel migration. Both would cost tens of millions of dollars (in 2022 dollars).

The Federal Emergency Management Administration (FEMA) did provide two grants for the 2011 storm event totaling $5 million, which is being used to install new culverts and turnaround areas at each end of the closure that will help prevent heavy storms and floods from damaging the area in the future and to provide safe areas for people to turnaround prior to reaching the washout area. That work is scheduled to start in summer 2023. Bids for the construction contract were solicited in December 2022.

An aerial view of the east fork of the Miller River, Old Cascade Highway, U.S. Route 2 and BNSF railroad. Larger view (1MB JPG). Map data: King County GIS ESRI 2013 Basemap.

What is being done to address safety and emergency access in the area

Western Washington faces growing wildfire risk as well as risk of other types of natural disasters such as flooding, slides, and severe winter weather events. The Department of Local Services is collaborating with the King County Office of Emergency Management, WSDOT, other state and local governments, and residents to explore ways to improve safety and resilience in the Skykomish Valley and prepare for future emergencies.

Road Services will update the community with new information on this website as it becomes available. Community members also can sign up for email updates: